The Secret Service under President Barack Obama has been scarred over and over by security breaches and public embarrassments. They began under Director Mark Sullivan and continued when Obama replaced him in March 2013 with Julia Pierson, who was grilled Tuesday by House lawmakers over the latest lapses. Details of almost all the breaches and missteps were uncovered by The Washington Post. Here are the highlights: November 2009: A Washington couple, Tareq and Michaele Salahi, crash Obama’s first state dinner. The Secret Service later acknowledges that officers never checked whether they were on the guest list. A photo emerges showing...